Defects in Be/Al composites prepared by direct WAAM using recycling beryllium swarf as raw material

Waste beryllium swarf was used as the reinforcement to fabricate 50 vol.% Be/Al composite wire through a pressure infiltration–rolling route, followed by wire arc additive manufacturing (WAAM). The microstructural evolution, defect characteristics, and mechanical properties of the as-deposited composites were systematically investigated, with particular attention paid to the origin of the large pore defects. During WAAM, the initially coarse beryllium swarf underwent pronounced remelting and microstructural reconstruction, forming fine beryllium dendrites that were relatively uniformly distributed in the deposited microstructure. Reducing the initial swarf size had little influence on the final deposited Be phase size, but significantly affected defect formation. Compared with the composite prepared from non-fragmented swarf, the sample fabricated from fragmented swarf exhibited improved surface quality and a markedly reduced defect area fraction, from 7.63% to 2.37%, together with a strong suppression of coarse pores. Droplet-scale observations indicated that these large irregular defects had already formed before droplet transfer and were less consistent with conventional lack-of-fusion defects. Combined with simplified theoretical analysis, the results suggest that local solutal Marangoni convection induced by Be-rich regions may contribute to bubble retention, coalescence, and growth during droplet evolution, thereby promoting the formation of coarse pore defects. The fragmented sample achieved a yield strength of 120.7 ± 12.1 MPa, an ultimate tensile strength of 166.9 ± 18.3 MPa, an elongation of 1.8 ± 0.6%, an elastic modulus of 140.8 ± 1.1 GPa, and a density of 2.27 g/cm³. These results demonstrate the feasibility of recycling beryllium swarf into high-volume-fraction Be/Al composite wire for WAAM and provide insight into defect control in arc-additively manufactured metal-matrix composites.